1. Field of the Invention
The present invention relates to an ink jet recording head that obtains recorded images by discharging ink to the recording surface of a recording medium.
2. Related Background Art
There has been practically provided an ink jet recording apparatus that forms images by the adhesion of the ink on the recording surface of a recording medium, which is discharged selectively thereto from plural ink discharge ports in accordance with recording data. For the ink jet recording apparatus of the kind, the ink jet recording head, which is selectively mounted on a carriage, is provided and arranged to face the recording surface of the recording medium and scan in the direction orthogonal to the conveying direction of the recording medium.
As shown in FIG. 8, an ink jet recording head 16 of the so-called side shooter type comprises, for example, the main body portion 18 formed by an ink supply portion 18B having an ink tank IT installed thereon, and an input terminal portion 18A electrically connected with a carriage portion (not shown) to receive a driving control signal group form the carriage portion; a supporting member 20 connected with the joining face 18b of a recess 18BG of the ink supply portion 18B of the main body portion 18; a recording element base plate 24 bonded to the upper face that serves as a second bonding face of the supporting member 20; and a printed circuit board 22 electrically connected with the recording element base plate 24 to supply the driving control signal group from the input terminal portion 18A.
The input terminal portion 18A and ink supply portion 18B of the main body portion 18 are formed integrally by resin, for example. On the upper face of the ink supply portion 18B of the main body portion 18 opposite to the portion where the ink tank IT is installed, an almost rectangular recess 18BG is arranged as shown in FIG. 8 and FIGS. 9A and 9B. The bottom face of the recess 18BG is made to be the joining face 18b where the supporting member 20 is bonded. A part of the joining face 18b is formed by the surface of a block piece 26 of aluminum alloy, for example. The block piece 26 is arranged in a metallic die and surrounded by resin when the main body portion 18 is formed. Almost on the central portion of the joining face 18b, there opens the thin and long end portion of the ink supply path 18a that induces ink from the ink tank IT.
As shown in FIG. 10 and FIG. 11, the recording element base plate 24 comprises the base plate 10 having an ink supply port 10c communicated with the opening end portion of the ink supply path in the ink supply portion; partition wall members 12 that form plural ink branch supply paths 12a arranged corresponding to heaters 10a serving as the ink heating portion on the base plate 10; and an orifice plate 14 having plural ink discharge ports 14a arranged in two line formation corresponding to each of the heaters 10a on the base plate 10.
For the recording element base plate 24, a silicon thin film is formed in a thickness of 0.5 mm to 1.0 mm, for example. Also, as shown in FIG. 9A, the surface of the recess 18BG of the ink supply portion 18B of the base plate, which is bonded to the joining face 18b by the application of a bonding agent, is provided with the ink supply opening portion 24c facing the orifice plate, which is extended in the arrangement direction of the ink discharge ports 24a. Further, on both sides of the base plate having the ink supply opening portion 24c between them, heaters (not shown) are arranged with designated gaps between them, respectively. The ink supply opening portion 24c is communicated with one end portion of the ink branch supply paths provided for the partition wall members. Each of the ink branch supply paths induces to each heater the ink that is supplied through the ink supply opening portion 24c. 
As shown in FIG. 8 and in FIGS. 9A and 9B, the printed circuit board 22 is electrically connected with each of the electrodes of the base plate for the recording element base plate 24. The printed circuit board 22 is provided with the containing portion 24B of the recording element base plate where the recording element base plate 24 is arranged, and a terminal portion 24A, which is arranged for the input terminal portion 18A of the main body portion 18. For the bonding of the printed circuit board 22 and the recording element base plate 24, the TAB (tape automated bonding) method is adopted, for example.
The supporting member 20, which is arranged between the recording element base plate 24 and the joining face 18b of the recess 18BG of the ink supply portion 18B, is formed to be flat and rectangular as shown in FIG. 8 and FIGS. 9A and 9B. Here, the same silicon material used for the recording element base plate 24 forms the supporting member 20, for example.
As shown in FIG. 9A, the supporting member 20 is provided with a second joining face 20Sa bonded to the surface arranged for the ink supply opening portion 24c of the recording element base plate 24, and a first joining face 20Sb bonded to the joining face 18b of the recess 18BG of the ink supply portion 18B. Also, the supporting member 20 is provided with a communication path 20a, which is extended to be thin and long in the longitudinal direction, in a position facing the ink supply path 18a arranged for the ink supply opening portion 24c of the recording element base plate 24 and the joining face 18b of the recess 18BG of the ink supply portion 18B. Further, the length of the shorter side and longer side of the supporting member 20 are the same as that of the shorter side and longer side of the recording element base plate 24, respectively, and the thickness of the supporting member 20 is substantially the same as that of the recording element base plate 24.
When arranging the recording element base plate 24 having the printed circuit board 22 connected therewith for the ink supply portion 18B, the first joint face 20Sb of the supporting member 20 is bonded, at first, to the designated position on the joining face 18b by use of bonding agent. Then, in continuation, as shown in FIG. 9B, the second joining face 20Sa of the supporting member 20 is bonded to the surface having the ink supply opening portion 24c arranged for the recording element base plate 24 by use of a bonding agent. Here, it is desirable to use a bonding agent having low viscosity and thin bonding layer to be formed on the contact face, and comparatively high hardness once cured.
With the structure thus arranged, when each of the heaters is heated on the base plate of the recording element base plate 24 with the supply of a heater driving control signal through the printed circuit board 22, ink is induced by way of the ink supply path 18a through the ink branch supply paths of the partition member. Then, ink is heated by each of the heaters to generate a bubble by means of a film boiling phenomenon, and along with the expansion of the bubble, ink is discharged from each of the ink discharge ports 24a toward the recording surface. However, there are the following problems encountered by the conventional example described above.
In other words, it is found that when the number of nozzles should increase and the length of the recording element base plate should be made larger still, the problems identified below occur sometimes irrespective of the case where the base plate is formed by the same silicon material used for the supporting member or formed by alumina or the like, the linear expansion coefficient of which is similar to that of silicon. Now, hereunder, the problems will be discussed more specifically in accordance with the properties of bonding agents used for bonding the supporting member and the recording element base plate.
(1) In a Case of a Thermal Curing Bonding Agent
When the recording element base plate and the supporting member are bonded by use of thermal curing bonding agent, the curing temperature is higher than the room temperature. In other words, the aluminum blocks of the main body portion, as well as the supporting base plate and the recording element base plate, are all bonded in a state of being expanded at a temperature higher than room temperature. Then, after bonding, as the temperature of recording head is lowered, each of the members is contracted. Generally, the linear expansion coefficient of the aluminum blocks is greater than that of the recording element base plate and the supporting base plate. Thus, the ratio of contraction thereof is greater when the temperature of the recording head is lowered. As a result, when the recording head returns to room temperature after bonding, the dimensional changes of the aluminum blocks are greater than those of the recording element base plate and the supporting base plate, hence generating stresses among the recording element base plate, supporting base plate, and the aluminum blocks. When the number of nozzles is small, and the length of the recording element base plate is small, the dimensional changes are also small when the temperature changes. The exertion of stresses is small accordingly. Therefore, if silicon or alumina is used for the supporting base plate, it is possible to minimize the amount of deformation of the recording element base plate because the use of such material can resist the occurrence of stresses. However, with the increase in nozzle numbers, the recording element base plate needs to become longer. Then, the difference between the dimensional changes of the recording element base plate, the supporting base plate, and the aluminum blocks becomes greater after curing, and the occurrence of stresses becomes greater accordingly. Consequently, even when silicon or alumina is used for the supporting base plate, it becomes difficult to resist the stresses thus exerted, and in some cases, the recording element base plate is deformed greatly. If such deformation takes place, the impact position of ink droplets from the recording head of an ink jet recording apparatus is caused to shift, resulting in the degradation of printed images or, further, the recording element base plate may be broken in some cases.
(2) In a Case of a Cold Curing Bonding Agent
When the cold curing bonding agent, which is cured at a temperature close to room temperature, is used for bonding the recording element base plate and the supporting member, there is no such problem as described above. However, if the temperature of the recording head rises during printing operation, the same problems take place. In other words, when the head temperature rises during the printing operation, the aluminum blocks, recording element base plate, and the supporting base plate are expanded, and the dimensions of each of them become larger. Particularly, the linear expansion coefficient of the aluminum blocks is greater than that of the recording element base plate and supporting base plate, and the dimensional changes are great. Thus, when the temperature rises, a difference in dimensional changes occurs between the aluminum blocks, and the recording element base plate and supporting base plate. As a result, stresses occur among the recording element base plate, supporting base plate, and aluminum blocks. When the number of nozzles is small, and the length of the recording element base plate is small, the dimensional changes are also small when the temperature changes. The exertion of stresses is small accordingly. Therefore, if silicon or alumina is used for the supporting base plate, it is possible to minimize the amount of deformation of the recording element base plate because the use of such material can resist the occurrence of stresses. However, with the increase in nozzle numbers, the recording element base plate needs to become longer. Then, the difference between the dimensional changes of the recording element base plate, the supporting base plate, and the aluminum blocks becomes greater after curing, and the occurrence of stresses becomes greater accordingly. Consequently, even when silicon or alumina is used for the supporting base plate, it becomes difficult to resist the stresses thus exerted, and in some cases, the recording element base plate is deformed greatly. If such deformation takes place, the impact position of ink droplets from the recording head of an ink jet recording apparatus is caused to shift, resulting in the degradation of printed images or, further, the recording element base plate may be broken in some cases. Now, therefore, the present invention is designed to solve the problems discussed above, and it aims at the provision of an ink jet recording head capable of printing high-quality images at all times without the deformation of the recording element base plate due to the difference between the temperature at which the recording element base plate is bonded and room temperature, or due to temperature changes at time of driving, especially when the recording element base plate is made longer due to an increase in the number of nozzles.
In order to solve the aforesaid problems, the present invention provides an ink jet recording head structured as described in paragraphs (1) to (10) given below.
(1) An ink jet recording head comprises:
a recording element base plate having an ink heating portion for heating ink, and ink discharge ports for discharging ink heated by the ink heating portion;
a main body portion having ink supply path for inducing ink from an ink retaining portion; and
a connecting member having a first bonding surface bonded to the main body portion, and a second bonding surface bonded to the recording element base plate. For this head, the connecting member is formed by material having a weaker stretching strength than that of the recording element base plate.
(2) The ink jet recording head referred to in paragraph (1) for which the relationship between the connecting member and the recording element base plate is arranged to satisfy the following formula (i):
Esxc2x7ts3xc2x7ws greater than Eaxc2x7ta3xc2x7waxe2x80x83xe2x80x83(i)
where
Es: Young""s modulus (dyn/cm2) of the recording element base plate
ts: thickness (cm) of the recording element base plate
ws: width (cm) of the recording element base plate
Ea: Young""s modulus (dyn/cm2) of the connecting member
ta: thickness (cm) of the connecting member
wa: width of the connecting member (cm)
(3) The ink jet recording head referred to in paragraph (1) or paragraph (2), for which the connecting member is formed from either a resin or a compound material of resin and metal.
(4) The ink jet recording head referred to in paragraph (1) or paragraph (2), for which the connecting member is formed from polyimide.
(5) The ink jet recording head referred to in any one of paragraphs (1) to (4), for which the connecting member is provided with electrode wiring for use in driving heat generating elements of the recording element base plate.
(6) The ink jet recording head referred to in any one of paragraphs (1) to (5), for which the connecting member is structured to laminate an electrode wiring with resin.
(7) The ink jet recording head referred to in any one of paragraphs (1) to (6), for which the recording element base plate and the main body portion are each provided with a portion for bonding the recording element base plate and the main body portion directly to each other.
(8) The ink jet recording head referred to in paragraph (7), for which the portions of direct bonding of the recording element base plate and the main body portion are arranged at plural locations.
(9) The ink jet recording head referred to in any one of paragraphs (1) to (10), for which the bonding center of the first bonding surface and the bonding center of the second bonding surface are arranged to shift in the horizontal direction.
(10) The ink jet recording head referred to in the paragraph (9), for which the bonding portions are arranged from a central area of the main body portion to a periphery thereof the following order: the area of in the direct bonding between the recording element base plate and the main body portion, the second bonding portion, and the first bonding portion.
With the adoption of the structure described above when embodying the present invention, the recording element base plate, which is arranged to obtain recorded images by discharging ink to a recording medium, is bonded and fixed to the main body, hence making it possible to provide an ink jet recording head capable of printing high-quality images at all times without deforming the recording element base plate due to the difference in the bonding temperature of the recording element base plate and the room temperature or due to the temperature changes at the time of driving, even if the number of nozzles increases and the recording element base plate is made longer.